/*
 * Copyright (C) 2008 The Guava Authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.google.common.testing;

import static com.google.common.base.Preconditions.checkArgument;

import com.google.common.annotations.Beta;
import com.google.common.annotations.GwtCompatible;
import com.google.common.base.Ticker;

import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicLong;

/**
 * A Ticker whose value can be advanced programmatically in test.
 *
 * <p>The ticker can be configured so that the time is incremented whenever {@link #read} is called:
 * see {@link #setAutoIncrementStep}.
 *
 * <p>This class is thread-safe.
 *
 * @author Jige Yu
 * @since 10.0
 */
@Beta
@GwtCompatible
public class FakeTicker extends Ticker
{

    private final AtomicLong nanos = new AtomicLong();
    private volatile long autoIncrementStepNanos;

    /**
     * Advances the ticker value by {@code time} in {@code timeUnit}.
     */
    @SuppressWarnings("GoodTime") // should accept a java.time.Duration
    public FakeTicker advance(long time, TimeUnit timeUnit)
    {
        return advance(timeUnit.toNanos(time));
    }

    /**
     * Advances the ticker value by {@code nanoseconds}.
     */
    @SuppressWarnings("GoodTime") // should accept a java.time.Duration
    public FakeTicker advance(long nanoseconds)
    {
        nanos.addAndGet(nanoseconds);
        return this;
    }

    /**
     * Sets the increment applied to the ticker whenever it is queried.
     *
     * <p>The default behavior is to auto increment by zero. i.e: The ticker is left unchanged when
     * queried.
     */
    @SuppressWarnings("GoodTime") // should accept a java.time.Duration
    public FakeTicker setAutoIncrementStep(long autoIncrementStep, TimeUnit timeUnit)
    {
        checkArgument(autoIncrementStep >= 0, "May not auto-increment by a negative amount");
        this.autoIncrementStepNanos = timeUnit.toNanos(autoIncrementStep);
        return this;
    }

    @Override
    public long read()
    {
        return nanos.getAndAdd(autoIncrementStepNanos);
    }
}
